The present invention relates generally to nose bar roll apparatus for veneer lathes, and in particular to such nose bar roll apparatus of large diameter which includes a knife gap adjustment means for automatically adjusting the knife gap between the nose bar roll and the knife blade during peeling in response to the reduction in log diameter and/or changes in the knife pitch angle.
Previously it has been proposed in U.S. Pat. No. 3,584,666 of Jensen issued June 15, 1971 to employ a nose bar roller which is powered by a motor and contacts the log ahead of the knife blade in a veneer lathe. The nose bar roller is moved into and out of contact with the log by a reciprocating carriage when an overload current is sensed in such motor due to an obstruction between the nose bar roller and the log, and to allow initial round-up of the log before peeling begins by cutting the log when the nose bar roller spaced away from such log. In addition, it has been proposed in U.S. Pat. No. 2,659,401 of Latimer issued Nov. 17, 1953 to adjust the pressure of the nose bar roller on the log to change the thickness of the veneer by employing wedges mounted on a motor driven screw shaft. In this regard, also see U.S. Pat. No. 3,680,613 of Daniels, et al issued Aug. 1, 1972 which also shows a motor driven screw shaft and cylinders for adjusting the pressure of the nose bar roll by manually operated control switches. However, in none of these patents is the gap between the nose bar roll and the knife blade adjusted automatically during peeling in response to reductions in the diameter of the log in the manner of the present invention.
Previously it has also been proposed in U.S. Pat. No. 3,473,585 of Cremona issued Oct. 21, 1969 and U.S. Pat. No. 4,263,948 of Hasegawa granted Apr. 28, 1981 to provide a veneer lathe with a knife gap adjustment means which employs a mechanical cam to adjust the gap between the pressure bar and the knife blade. This is accomplished in the Cremona patent by a double-acting piston which moves the cam wedges over cam follower rollers in order to adjust the pressure bar carriage attached to such wedges between a round-up position and a selected one of a plurality of different peel thickness positions corresponding to stops which are selected for changing the thickness of the wood veneer. Hasegawa shows a somewhat similar technique for changing the knife gap but employs an eccentric cam which is rotated by either a rack and pinion gear arrangement or a lever in order to adjust the pressure bar roll or a plurality of spaced drive roll discs which extend through slots between the pressure bar. The drive roll discs are adjusted in order to cause the spikes of the drive roll to extend further into the log as the diameter of the log decreases in order to compensate for fewer spikes being engaged with the log. This mechanical adjustment of the knife gap by use of the cams is not satisfactory because such gap adjustment cannot be readily changed to compensate for different types of wood or to take into account varying pitch angles of the knife blade. These problems are overcome in the present invention by employing an electronic control for the gap adjustment means for automatically adjusting the gap in response to decreases in the log diameter and changes in the knife pitch angle during peeling.
It has been previously proposed in U.S. Pat. No. 3,207,194 of Hedberg, et al granted Sept. 21, 1965 to mount a nose bar roll on needle bearings and to drive the nose bar roll by a motor coupled to one end thereof by a chain belt. There is no knife gap adjustment during peeling in response to decreases in the diameter of the log. Apparently, the nose bar roll of Hedberg is of a conventional type having small diameter of about 5/8 inch and is not of a large diameter of at least 1.5 inch and 15 times the veneer thickness in the manner of the nose bar roll used in the present invention which is typically about 3.75 inch in diameter. As a result, such conventional nose bar roll does not tend to lose contact with the log as the diameter of the log decreases during peeling as is true of the large diameter nose bar roller of the present invention. Thus, there is no reason to adjust the gap between a conventional small diameter nose bar roller and the knife during peeling in response to the reduction in diameter of the log to maintain contact with the log and to maintain the proper pressure on the log for the production of high quality veneer of a substantially constant thickness, in the manner of the present invention.
The veneer lathe apparatus of the present invention provides automatic knife gap adjustment to reduce the gap between a large diameter nose bar roll and the lathe knife during peeling in response to a reduction in log diameter and to changes in the knife pitch angle which results in several advantages. As a result of such knife gap adjustment, a large diameter nose bar roll is maintained in contact with the log at the proper pressure during peeling, to provide a better quality veneer whose thickness stays substantially constant. In addition, this automatic knife gap adjustment is provided by means of an electronic control in the present invention which is more versatile than mechanical controls using cams since it can compensate for different types of wood and different wood conditions quickly and easily for more efficient production. Further, the invention eliminates the need for excessive pressure force to be applied to the log by the nose bar roll initially for large diameter logs to compensate for the decrease in such force as the log decreases in diameter during peeling. Such excessive initial pressure force tends to damage the veneer. In addition, the automatic gap adjustment apparatus of the present invention prevents spin-outs of the log from the drive spindles engaging the opposite ends of such log since the nose bar roll applies a more uniform pressure to the log during peeling. Also the large diameter nose bar roll prevents jamming and reduces dulling of the knife to increase the useful cutting time of the knife between sharpenings. Such nose bar roll is powered to provide auxiliary drive for rotation of the log, thereby reducing the drive which must be supplied by the spindles to further prevent spin-out. This also enables the log to be peeled to a smaller minimum core diameter.